The present invention relates to a drive system for a wind turbine.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Besides slow-running gearless direct drive systems and medium-fast-running drive trains with one- or two-stage gearboxes, fast-running drive trains which have three or more gearbox stages and which are conceptually fundamentally different are also used in wind turbines at present. These drive train concepts each embrace a number of variants with modular, open and partially integrated system architecture.
Essentially a heavy machine drive train comprises system components, such as power connection elements, motors or generators, couplings, gearboxes and drive shafts. Converters are frequently provided lineside. Brakes are often provided in the form of mechanical brakes on a fast-running shaft between gearbox and motor or generator, as braking torques are smaller there because of the gear ratio.
In systems with driven components, such as wind turbines or mill drive systems, forces which are undesired and which can damage or destroy components also occur. These may be conditioned by the application or may be inherent to the system. In particular, couplings between gearbox and motor and/or generator, drive shafts and gearbox are frequently exposed to damaging torsional and vibrational forces as well as bending stresses within drive and output shafts which at least have to be reduced. In some cases this can be achieved by incorporating gearbox, motor or shaft bearings that reduce forces or vibrations.
In wind turbines in particular, stresses conditioned by the effect of wind occur in addition to normal machine drive forces. Sometimes highly irregular wind strengths or directions can introduce considerable tensile, compressive and lateral forces in the main shaft, main bearing, machine frame and drive train. These forces act as undesired additional or special forces. System components or parts must then resist these additional or special forces. Examples of special events to be considered include gusts of wind that occur only once every few decades, braking loads, shedding of large loads or power failures. Such special events can cause considerable deformations in main frames of wind turbines. This leads for example to movements in foundation bearings for drive train components. These movements can in turn induce constraining forces in the drive train which can result in severe damage to bearings and other force-conducting parts of a drive train of a wind turbine.
It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved reliable, energy-efficient and easy-to-maintain drive system for a wind turbine.